This invention relates to a probe microscope for analyzing the surface state of a material by detecting interatomic forces (AFM: Atomic Force Microscope) or magnetic forces (MFM: Magnetic Force Microscope) acting between materials or tunnel currents (STM: Scanning Tunneling Microscope) occurring between materials.
Since being devised by G. Binning et al (Physical Review Letter Vol. 56 p. 930 1986), the atomic force microscope (AFM), which is a type of probe microscope, has been considered promising as new means for observing surface shapes of insulating materials, and research into these microscopes has been being advanced. This AFM will be discussed as an example. Among AFMs there are types for use with relatively small specimens which scan the specimen side over a plane with respect to a detecting part and types for use with large specimens which scan a detecting part with respect to the surface of the specimen; FIG. 7 is a block diagram of a type wherein the detecting part is scanned with respect to the specimen. This apparatus will now be described with reference to FIG. 7.
A machine section is disposed on an anti-vibration bed 1 which dampens vibrations coming from the floor; the machine section has a stage 4 by which coarse positioning in three dimensions (X, Y, Z) of a specimen 3 is performed with a box frame 2 as a reference, and a detecting part 5 is mounted via a scanner 6 on the box frame 2 facing the specimen 3. The scanner 6 moves in three dimensions and based on X, Y scanning signals from an X, Y scanning system 7 scans the detecting part 5 over the specimen 3 in the X, Y plane. The detecting part 5 consists of a device for optically measuring interatomic forces acting between the specimen 3 and a detecting chip with a sufficiently sharpened end as displacements of a spring element 71 on which the detecting chip is mounted. The Z axis of the scanner 6 is operated by a Z follow-up signal outputted by a Z axis servo system 10 so as to keep the value of a detection part signal 9 outputted by the detecting part 5 constant at all times. The Z axis follow-up signal and the X, Y axis scanning signals are processed through image processing means (a computer) 12 and displayed on a monitor 13.
Conventionally the scanner 6 consists of a piezoelectric element. As shown in FIG. 5, a piezoelectric element 51 is deformed by a voltage being impressed on electrodes 52 disposed on both sides of it and can be made to extend and contract by the direction of the impressed voltage being changed relative to the direction of polarization of the piezoelectric element. Normally, PZT (titanium lead zirconate) is mainly used as the material of the piezoelectric element. As shown in FIG. 6, the displacement of this PZT piezoelectric element with respect to the impressed voltage is non-linear (has hysteresis). As a result, to cause a displacement 2L twice the size of a certain displacement L does not necessarily require twice the voltage. In the terms of FIG. 6, V.sub.b .noteq.2 V.sub.a.
Consequently, because in the AFM system both the X,Y scanning signal 8 and the Z follow-up signal 11 used in the image processing are voltage values, an error occurs with respect to the actual specimen shape. Here, because the voltage variations of the X and Y axes are fixed, the error in these directions can to some extent be corrected by computation; however, correction of the Z axis which is varied irregularly by the specimen surface is more difficult than correction of the X and Y axes.
To solve this problem, it is possible to reduce the error by measuring the amount of displacement with other detecting means and performing image processing based on those values. However, in types such as the AFM system described above which measure especially large specimens, because this involves further incorporating a separate displacement detecting means onto the end portion of the scanner 6 where the detecting means 5 is disposed, severe restrictions are placed on the form of the separate displacement detecting means (it must be extremely small).
This invention has as an object the provision of a probe microscope wherein separate displacement detecting means is used as means for reducing the error, coming from the non-linearity of the piezoelectric element, between the results after image processing and the actual shape, of a constitution having means for incorporating this displacement detecting means into the system without there being restrictions on its form such as that it must be made extremely small.